When the mass of (1) X, y and m is the same, m completes the reaction first, then y, and finally x completes the reaction, so it can be judged that the activity of the three metals is M > Y > X；;

(2) According to "three different metals X, Y and M with the same mass react with enough dilute sulfuric acid with the same solute mass fraction to generate XSO4, YSO4 and MSO4", we know that their valences are the same; Then according to the mass of hydrogen produced by the complete reaction of a certain amount of metals = the relative atomic mass of valuable metals x the mass of metals. Because the mass and valence of metals are the same, the relative atomic mass of metals is proportional to the amount of hydrogen released by the reaction, so the relative atomic mass of the three metals is y > x > m；;

(3) Iron reacts with dilute sulfuric acid to generate ferrous sulfate and hydrogen, and the chemical equation of the reaction is: Fe+H2SO4 = FeSO4+H2 ↑;

So the answer is:

( 1)M > Y > X； (2)Y > X > M； (3)Fe+h2so 4 = feso 4+H2↑；